With development of information and communication technologies and spread of the Internet of things (TOT), interest in a wearable device has been growing. The wearable device refers to a computer device that can be worn on a user's body, and includes various sensors. By computing data from various sensors and grasping what situation a user is in through the wearable device, it is possible to provide various IoT-based services. Therefore, researches have been actively conducted on how to use the wearable device in recognizing environments of a user. Recently, various kinds of wearable device have been released as products which are commercial but not for research purposes.
A conventional technique for grasping a user's activity or location information is classified according to sensors used therein, and the used sensor is also classified into two types according to positions of the sensor. A first technique refers to a method of using the sensor depending on an infrastructure where the sensor is installed in a space. In a large space, an inexpensive sensor such as a passive infrared sensor for intruder detection or an ultrasonic sensor is installed, or recording is performed with a camera to collect data, and a wireless signal transceiver is used for tomography. In this method, a user's location can be grasped only in a place where the sensor is directly installed. A second technique refers to a method in which a user carries a device mounted with a sensor. In this method, a user attaches the sensor to user's body, carries a smart phone, or wears a wearable device, on conditions that the sensor is near user. An inertial sensor for sensing acceleration or rotational angular velocity is generally used, and a module for reading a radio frequency identification (RFID) signal, a network module for collecting a wireless fidelity (Wi-Fi) signal, or the like may be used. For example, an RFID tag is used, or a W-Fi module of the smart phone is used.
However, the foregoing conventional techniques have problems as follows. First, the method of installing the sensors in the infrastructure requires necessary sensors to be mounted all over a house, and thus a practical problem arises in relation to costs and installation. Although concept of smart homes has been introduced with the spread of the IoT, it does not reach a level of installing the ultrasonic sensors or the cameras throughout the house yet, and may cause additional costs even if possible. Second, the method of using the smart phone has currently been widely used, there is a limit when a user is located inside the house. For example, the smart phone may not directly obtain information about a user's motion since it is likely to be charging or be not carried while user is located inside the house. Last, the conventional location grasping method of using the wearable device has a problem of consuming much power since it periodically collects a Wi-Fi signal. Since the wearable device has relatively small battery capacity, it is not suitable for collecting the Wi-Fi signal and grasping a user's location. Further, the wearable device cannot sufficiently show its ability in terms of hardware and software since it has a limited size.